ROV Implementations

4.7.1 Selecting between Penetrator and Connector

The ordered tether cables (150 and 300 meters) comes with penetrators attached. Only apply thread seal and mount it to the ROV. The disadvantage of penetrators is that the cable cannot be swapped fast, and when carrying the heavy ROV, the cable is often in the way and makes the moving harder.

The alternative to this is using connectors, making it possible to switch cables fast and discon-nect the cable when moving. Mounting the condiscon-nectors take hours of work, but the upside with them is more significant than the downside; connectors was therefore added to the two new tether cables. Initially, we wanted connectors for our side-scan sonar, but since the electronic box for the side-scan was not potted, we could not place it outside of the ROV and send signals via Ethernet into the ROV. Therefore the electronic box had to stay inside the ROV and two cables with a high-frequency signal going inside the ROV; due to recommendation from the manufac-turer that the connector could make noise on the signal, the connector was not chosen.

4.7.1.1 Implementation

Soldering the connector requires some experience with soldering; this is because the wires had to be as short as possible to get the connector more waterproof. When soldering the connector, it is also essential to keep in mind the temperature on the soldering iron and the amount of time used to solder the connection. The isolation on each wire tends to melt fast. Figure4.25shows the soldered connector. The colour code for the pin is shown in Figure4.26, which corresponds to the male side of the connector, which comes pre-soldered.

Figure 4.26: Female connector to ROV

The epoxy "3M™ Scotch-Weld™ uretanlim 620NS" is used for sealing, and it is chosen for its flexibility and softness. Harder epoxies used in the earlier iteration of this projects tend to crack. The epoxy was heated with a heat gun to get a smoother finish and make the epoxy more fluid. A needle was used to poke air bubbles out. Figure4.27shown the sealed penetrators.

Figure 4.27: Penetrators sealed with epoxy

4.7.2 Sensor modularity

One of the potential use of the ROV is to collect sensor data with a different type of sensor at-tached to the ROV. Sensors can be expensive, or they are just needed for a short time. By making the sensor system modular, these can be easily attached and removed for other projects. These sensors will primarily be connected to the one ArduinoSensor. Considering the number of pro-tocols and possible connection method of a sensor, not all can be considered. A selection of easily accessible ways to read sensor data is made and shown in4.1.

Type Pin

Analog A0

Analog A1

Analog A2

Analog A3

Digital D2

Digital D3

Software UART 11, 12 Table 4.1: Modular sensors

As described in the Settings page4.4.1.2, adding a new sensor to the system requires it to be connected and adequately sealed physically. Then a name for the sensor, its origin (ex: Ar-duinoSensor) and port it is attached to is typed in the GUI. The GUI will make the REST-API

cre-ate and send a payload (Payload A1/A2, Figure4.28) to the Raspberry Pi, where it is forwarded to its destination. The Raspberry Pi will also store the variable name for filtering out erroneous sensor data. When it arrives at its destination, the given port will check its availability and start sending data with the given variable name. The new sensor data will be added to payload B along with all other sensor data. This process is showed in Figure4.28.

Figure 4.28: Modular sensor flow

4.7.3 Lights

From the previous ROV only one light was working, and before testing it properly, we found wa-ter leaks inside. Therefore four new lights were purchase and mounted. With four light sources, the lighting should be more even for the video, and in total, the four light can produce 6000

lu-mens [52]. It should consume around 60 watts with maximum brightness, meaning at 12 volts, the current should be about five amps. Although the lights are rated for 10-48 volt input power, the voltage it will be connected to is 12 volt. The reason for that is the variance in the voltage from the batteries, which should be around 48 volts. The lights are depth rated for 500 meters and are using a PWM signal to control the brightness. Brightness can be dimmed from 1100 µS (off) to 1900µS (brightest). The ground from 12 volt needs to be connected to the ground on RPi to control the light; else, it will be unstable due to grounds with different potentials. The PWM signal needs to be connected to a pull-down resistor to the ground to avoid floating output signal at startup.

Figure 4.29: Lumen Subsea Lights R2 [52]

4.7.4 IMU

The IMU is used to estimate the angular position of the ROV. The angular position is required for controlling the trim angle and is essential when evaluating the ROVs behaviour.

Choice of IMU and Sensor Fusion algorithm

The IMU from the previous project had to be replaced as the USB connector fell off, and the IMU is out of production. The Adafruit 9-DOF was chosen as it is easily available and is accurate enough for its purpose.